I have the IPV V2 and there will be a difference. If you set a wattage and change resistance the voltage will have to change. Basic ohms law. Running high wattage on the kayfun or any atty for that matter can melt the insulator. Wish they had come out with a silicone type insulator but they are all plastic. Kidney puncher and Fat Daddy's have replacements. The Kayfuns were not built for high wattage or for big clouds. Drippers do a better job of that.
As a reubuilder you should know ohms law and battery safety. Sorry but i made a promise to someone to make this speech to folks that are new to rebuilding. Would hate for you to have a bad day.